Process of preparing salt-free n-acyl taurines



United States Patent PROCESS OF PREPARING SALT-FREE N-ACYL TAURINESLeslie M. Schenck, Mountainside, NJ assignor'to General Aniline & FilmCorporation, New York, N.Y.,,a corporation of Delaware No Drawing. FiledDec. '30, 1958, Ser; No. 783,681"

12 Claims. (Cl. 260-401) U-.S; Patent No; 1,932,180, severalprocessesare-described' for the preparation of suchsurface active materialsbutthe only process which hasup tothe presentbeen employed commercially isthat wherein an acid-chloride is reacted in aqueous medium with aZ-aminoalkane sulfonic acidin thepresence of an acid neutralizer suchasv caustic soda.

salt, eig; sodium chloride (or potassium chloride if caustic potash isused as acid neutralizer) as awby-product'.

Thepresence of such salts with the N-higher acyl taurine is highlyundesirable and disadvantageous-forj a num'ber'of reasons. Not only dosuch salts have asubstantial corrosive efiect inthe packaging andhandling of detergents and'other surface active-compositionscon tainingsuch acyl taurines, but theyalso exert a strong adverse effect on thelathering; detergent and other surface active properties of mixtures ofsuch acyl taurines with soap. The acyl taurines' are verygood'limesoapdispersants and the combination of minor amounts thereof withordinary fatty acid soaps in detergent andbuilt-soap formulationsresults in highly effective-detergent properties; particularly inhard'water. However, for such com binations to'have optimum properties,the' N-higher-acyl taun'n'epresent therein should-have a low saltcontent.

The'presence'of this salt in' a number of. commerciallyavailable N-acyltaurines, has'been identified as amajor reason for the unduly highhygroscopicityof such products: Thepresence of such salt is alsoundesirable when theN-acyl taurine is to be employed in certainemulsion'polymerization reactions and in other uses.

A numb'er of proposals have been made in the prior art" for theproduction of salt-free N-liigher acyl taurines,

some of which involvethe use ofa' differentmethod of reaction or ofdifferent reactants in'the produ'cti'onof such tauri'nes, and othersofwhich involve expensive an'cl'ditficult separation methods,

Itis an object of this invention to providea process for producing asalt-free N higher acyl taurine which will not be subject to" the abovedisadvantages. An-

other objectof this invention is the provision of' a proc--ess-for'p'roducing wsalt-free N-higher acyl taurinefrom.

an aqueous slurry containingisuch: taurine in combination with a watersoluble salt.- va'nt'ages will appear as the description proceeds;

The attainment: of the aboveobjectsis madepossible by the presentinvention which includes a process com- This inherently produces;v inaddition tothe N-higher'acyl taurine, a considerable quantity of Otherobjectsan'claadsprising addingto an aqueousslurry containing (A)N-higher. acyltaurine of the formula R'CONR"CHR--CHRSO M wherein one Ris selected from the group consistingof i H and methyl and the other Ris H, R is selectedfromv the group consisting of H and hydrocarbonradicals of the group consisting of H, alkali metal, alkaline earthmetal, ammonium. and amino, and (B) a water soluble salt selected fromthe group consisting of the alkali metal chlorides and sulfates, a waterinsoluble compound;

C selected from the group consisting of aliphatic and alicyclicmonocarboxylic acids of 8 to 24 carbon atoms and their esters in anamount sufficient to form a compatible solvent systemwith said taurine(A),-heating the resulting mixture to distill off the water, and thenseparating the crystallized salt B from the mixture at a temperatureabove the solidification point of the A and C solvent: system;

An outstanding advantage of the process of this invention is that it isoperable on the commercially avail able N-higher acyl taurines producedby the Schotten- Baumann reaction between a higher fatty acid chlorideand a taurine, and may be carried out by soap manufacturers themselvesin readily available equipment. The product produced by the aboveprocess is a mixture of the acyl taurine Withthe higher molecular Weightcan boxylic acid or ester which may be employed as such to saponify thecarboxylic acid and produce its soap-in. Such soa'p compositions areuseful directly as Sill]; toilet soaps and other cosmetic applicationsin liquid or solid form and can readily be formulated into barsor'cakes. If desired, the resulting combination of soap and N-higheracyl taurine may be spray dried or drain dried to produce a flake orpowder detergent and may be combined before or after such drying withcommon. builders, stabilizers and thelike for the production ofheavy'duty built detergent compositions. Common compon'ents of suchbuilt compositions include alkali metalphosphates and polyphosphates,silicates, carbonates, and sodium -ca'rboxyinethyl cellulose.

Since the-present process is performed at moderatetemperatures; nodiscoloration of product or reactants is experienced and the originalpurity of the intermedi ates "is representative of the final product,excluding those impurities that are insoluble in the dehydrated solutionand? thereby; removed during the; processing. Highly specializedequipment required by the prior art to maintain the necessary reactionconditions for'the production of the desired salt-free N-higher acyltaurines is no longer'necessary. The operability of the present processis surprising and unexpected in view of the anticipated foamingwhichwould normally be expected to occur in a fatty acid-syntheticdetergent-soap and water formulation of'the type involved in the presentprocess. t

If a final product is desired which must be not only salt-free but alsosubstantially pure, the higher carboxylic acid employed to form acompatible solvent system with theacyl taurine maybe convenientlyremoved by distillation.

The process of this invention is applicable for'the treatment of anyaqueous slurry containing the N-higher. acyl taurine and a water solublesalt, regardless of its manner of production. The N-higher acyl taurineswhich are produced in salt-free form in accordance with this.

invention may in general be ascribe'd'tlie formula givti" Patented Mar.1-, 1-961 above. Such acrylated taurines may be prepared by reaction ofa taurine salt containing at least one N-bonded hydrogen atom with ahigher molecular weight acylating agent of the formula R'COOH or R'COCl.Those acylating agents particularly preferred are the higher free fattyacids of 12 to 18 carbon atoms (R' is 7 to 17 carbon atoms). Asgenerally representative of higher aliphatic and alicyclic carboxylicacids operative in the instant invention, there may be mentionedcaprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid,palmitic acid, stearic acid, oleic acid, ricinoleic acid, linoleic acid,undecylenic acid, tall oil acid, acid mixtures from various naturalplant and animal oils such as olive, tallow, castor, peanut, coconut,soybean, cotton seed, ucahuba, linseed, cod, herring, menhaden,neatsfoot, sperm, palm, corn, butter, babassu, kapok, hempseed, mustard,rubberseed, rape, sunflower, sesame, acids from the oxidation fractionsof petroleum, and from oxoaldehydes, naphthenic acids, abietic acids,and the hydrogenated derivatives of such acids and acid mixtures. Otheracids which may be employed include alkyl benzoic acids such as dodecylbenzoic acid, nonyl bcnzoic acid, octyl benzoic acid, alkyl naphthoicacids such as nonyl naphthoic acid, and the like.

The above described carboxylic acid acylating agents are accordinglyrepresentative of the aliphatic, alicyclic and aromatic hydrocarbonradicals of 7 to 23 carbon atoms which may be employed as R in the aboveformula. Such carboxylic acid acylating agents (e.g. RCOCl) are reactedwith taurines of the formula to produce the acylated taurines treated inaccordance with the present process. In this formula, R" may representhydrogen, methyl, ethyl, isopropyl, butyl, hexyl, cyclohexyl, phenyl andthe like, and M may represent hydrogen or a salt-forming cation such asan alkali metal, e.g. sodium, potassium or lithium, an alkaline earthmetal such as calcium, magnesium or barium, ammonium, or an amine suchas mono-, dior triethanolamine, cyclohexylamine, guanidine or the like.Thus, by way of example only, the following specific Z-aminoalkanesulfonic acids may be employed as such or in the form of their salts forreaction with the above defined carboxylic acid acylating agents:taurine, N-methyl taurine, N-ethyl taurine, N-propyl taurine,N-isopropyl taurine, N-butyl taurine, N-amyl taurine, N-hexyl taurine,N-cyclohexyl taurine, N-phenyl taurine, N-methyl-Z- methyl taurine,N-methyl-l-methyl taurine, and the like.

The aqueous slurries treatest in accordance with the present process,should in general be sufiiciently fluid to be readily workable. Ingeneral, in such slurries, the acylated taurine would be present inconcentrations of about 15 to 40% by weight, 35% slurries being thosemost readily available on the market. In such slurries, the watersoluble salts usually present as a result of the method manufacturingthe acylated taurine may be present in proportions as high as 30 to 35%of the weight of the acylated taurine, 20 to 25% being common. It willof course be understood that the present process is also operative forremoving smaller proportions of salt, e.g. as little as 5% or less orhigher proportions, e.g. up to 50% or more, of the weight of theacylated taurine. The salt most commonly present in such slurries issodium chloride, usually accompanied by smaller proportions of sodiumsulfate. However, potassium chloride and potassium sulfate may also bepresent for other reasons or because potash was employed in the reactionfor producing the acylated taurine. The acylated taurine slurriescommonly available normally have a pH of about 7 to 8, but the processof this invention is operative not only on these slurries but on thoseof a much higher acidity or alkalinity.

As stated above, the process of this invention requires the addition toan aqueous slurry as above described of 4 a water insoluble compound(component C) selected from the group consisting of aliphatic andalicyclic monocarboxylic acids of 8 to 24 carbon atoms and their estersin an amount sufficient to form a compatible solvent system with theacylated taurine (component A).

The preferred component C for use in the present process is a freehigher fatty acid of 12 to 18 carbon atoms which may be saturated orunsaturated, branched but preferably straight. Other aliphatic andalicyclic monocarboxylic acids which may be employed as component C inthe present process include those disclosed above as operative acylatingagents (R'COOH) with the exception of the alkyl benzoic and alkylnaphthoic acids since component C and component A (acylated taurine)must be mutually soluble to form a compatible solvent system meltingbelowthe boiling point of water and boiling above the boiling point ofwater under the conditions of the distillation required in the presentprocess. The methyl, ethyl, propyl or glyceryl esters of such acids mayalso be employed. It will be generally found that the amount ofcomponent C necessary to form a compatible solvent system with componentA at the temperature of separation of the crystallized salt from themixture above the solidification point of such system will be at leasttwice theweight of said component A (acylated taurine), and will ingeneral range from about 2 to 6 parts per part by weight of component A.Higher porportions may be employed but are uneconomical except where alarger proportion of soap is desired in the final product as obtained bysaponification of component C in situ following removal of the water andsalt in accordance with the present process.

After addition of the required amount of component C to the aqueousslurry containing the acylated taurine and water soluble salt, theslurry is heated to the boiling point to distill off the water. Thedistillation maybe carried out at super or sub-atmospheric pressure butit is preferred, in the interests of simplicity and economy to operateat atmospheric pressure. Surprisingly, the boiling proceeds without theanticipated foaming. At normal atmospheric pressures, temperatures ofabout to C. are preferred for optimum simplicity, economy and rate ofdehydration. A small flow of air or inert gas over the surface of theboiling slurry is desirable but not essential to aid in removal of watervapor. An inert gas such as nitrogen or carbon dioxide is in such casepreferred to prevent possible discoloration of the acylated taurine.Lower temperatures of boiling may be em ployed at sub-atmosphericpressures.

The distillation is continued until substantially no more water isremoved, as indicated by substantial cessation of loss of weight of thedistillation vessel. The duration of the distillation process will ofcourse in any particular instance depend upon the amount of slurry beingtreated, the temperatures and pressures employed, and the like. Underusual conditions and batch sizes, a duration of about 1 to 3 hours issufficient. At the completion of this distillation step, substantiallyall of the salt has been precipitated in the distillation vessel whichmay still contain a small amount of occluded water.

During the boiling operation and as the water is removed from theaqueous slurry, the water soluble salts crystallize out and may, aftercompletion of the distillation step, be readily separated from theremaining mixture at a temperature above the solidification point of thecompatible solvent system of components A and C contained in themixture. system is maintained in liquid form to permit removal of thecrystallized water soluble salt originally dissolved in the aqueousslurry. The separation of the salt may be carried out in any desiredmanner as by filtration, centrifugation, decantation, or the like. Inpractice, it would be desirable to filter or centrifuge the mixtureimmediately after all the water has been removed and while it is stillhot and in liquid condition. Generally, the separa- Stated otherwise,such solvent.

abraded.

tio nfwould be carried out; at about-130 '6. although any temperaturewould *be suitable provided it is above the solidification point of thesystem throughout the separating operation.

By the present process, there is thusobtained :from the original.aqueous :slurry asusbtantially homogeneous mixture or solution ofcomponent Aand component .C. This Product is advantageouslysubjected tosaponification with caustic soda or potash to produce the soap ofcomponent C insitu together-with the acylated'taurine. However, ifdesired, component C may beseparated from the acylated taurinebydistillation or the like.

The following examples, in which parts are byweight, unless otherwiseindicated, are only illustrative of the instant invention and are not to.be regarded as limitative. In these examples, all parts and proportionsof fatty acid amides are determined by the methylene blue analyticalmethod described in Nature, 160, '759 (1947) and Trans. Faraday Soc. 44,226- 23911948). The tallow fatty acid contains, by weight, approximatelymyristic, 43% 'palmitic, 9% stearic, 30% oleic, and 8% linoleic acids,and the coconut fatty acid contains, approximately, 8% caprylic, 7%capric, 49% lauric, 17% myristic, 9% palmitic, 2% stearic, 6% oleic, and2% linoleic acids.

Example 1 Twelve hundred grams of an aqueous commercial slurrycontaining 300 g. of sodium N-methyl-N-coconut fatty acid taurate and 69g. sodium chloride is admixed with 900 g. commercial coconut fatty acidand gradually heated to 130 C. with agitation in an open vessel with aloss of 685 g. water, after which crystallized salts are immediatelyremoved by filtration. The filtrate contains by analysis 300 g. of saidtaurate, 0.63 g. sodium chloride, and 17.3 g. water, in addition to thefatty acid.

Upon saponifying the fatty acid with caustic to convert same to thesodium soap in situ, the resultant detergent-soap mixture can beconverted to bars with excellent detergent properties.

Example 2 One hundred fifty grams of an aqueous commercial slurrycontaining 52.5 g. sodium N-methyl-N-oleoyl taurate and 10.2 g. sodiumchloride is admixed with 100 g. coconut fatty acid and heated to 135 C.to remove 71 g. water by atmospheric distillation, after which theinorganic suspension is immediately removed by filtration, and thefiltrate analyzed as containing 52.0 g. of said taurate, 0.1 g. sodiumchloride, and 3.0 g. water in addition to the fatty acid.

Example 3 One hundred fifty grams of an aqueous commercial slurrycontaining 52.5 g. of sodium-N-methyl-N-oleoyl taurate and 10.2 g.sodium chloride is admixed with 100 g. coconut fatty acid and dehydratedat 55 C. by heating under reduced pressure of about 150 mm. of Hg untilno more water distills over. The crystallized salts are then immediatelyremoved by centrifuging, and the clear oil effluent found by analysis tocontain in addition to said fatty acid 52.5 g. of said taurate, andsubstantially no sodium chloride or water.

Example 4 Two hundred forty grams of an aqueous commercial slurrycontaining 24.6% by weight sodium-N-methyl-N- coconut fatty acid taurateand 5.75% by weight sodium chloride is added to 160 g. tallow fatty acidand the mixture dehydrated by heating to 140 C. under a stream ofnitrogen until substantially no more water distills over The inorganicsuspension is then immediately removed by filtration, and the product,235 g. analyzed as containing, in addition to the tallow fatty acid andsome water, 25.1% by weight of said taurate and 0.291% by weight sodiumchloride.

g I Example 5 p Four'hundred parts by weight of an aqueous commas cial,slurry containing 25% by weight of ,sodiumeN- methyl-N-ftallow fattyacid. taurate and 6.82% by weight sodium chloride are admixed at 60 C.with 200 parts by weight of commercial tallow fatty acid. The resultantslurryis fed into a continuous evaporator .opcratingat 1:25 to 135 .,C.,at a rate allowing substantially complete dehydration and .theessentially anhydrous fluid effluent immediately freed ofsuspendedinorganic salts 'by continuousfiltration:toyield a product containingparts .by weight of said taurate, 1 part by weight of sodium chlorideand 19 parts by weight of water, in ad. dition :to ,the vtallow fatty:acid.

V Example -6 The process of Example 2 is repeated, except that theinitial slurry contains the corresponding potassium taurate salt andpotassium chloride. Similar results are obtained.

Example 8 Six hundred parts by weight of an aqueous commercial slurrycontaining by weight 25% of sodium-N-methyl-N- coconut fatty acidtaurate and 5.75 by weight of sodium chloride is admixed with 450 partsby weight of coconut fatty acid and heated to C. to distill out substantially all the water originally contained in the slurry, after whichthe precipitated salts are immediately removed by filtration, and thecoconut fatty acid is removed from the filtrate by distillation in vacuoto leave a residue analyzing parts by weight of said taurate and 0.3parts by weight of sodium chloride. V

Example 9 The process of Example 6 is repeated except that the tauratein the initial slurry is sodium-N-butyl-N-palmitoyl taurate. Similarresults are obtained.

This invention has been disclosed with respect to certain preferredembodiments, and various modifications and variations thereof willbecome obvious to the person skilled in the art. It is to be understoodthat such modifications and variations are to be included within thespirit and purview of this application and the scope of the appendedclaims.

I claim:

1. A process comprising adding to an aqueous slurry containing (A) anN-higher acyl taurine of the formula of the alkali metal chlorides andsulfates, a water insoluble compound C selected from the groupconsisting of aliphatic and alicyclic monocarboxylic acids of 8 to 24carbon atoms and their esters in an amount sufficient to form acompatible solvent system with said taurine A, heating the resultingmixture to distill off the water, and

then separating the crystallized-salt B from the mixture at atemperature above the solidification point of the A and C solventsystem.

' 2. A process as defined in claim 1 wherein component A issodium-N-methyl-N-coconut fatty acid taurate.

3. A process as defined in claim 1 wherein component A issodium-N-methyl-N-tallow fatty acid taurate.

4. A process as defined in claim 1 wherein component A issodium-N-oleoyl taurate.

5. A process as defined in claim 1 wherein compm nent A issodium-N-cyclohexyl-N-palmitoyl taurate.

6. A process as defined in claim 1 wherein component C is a free fattyacid of 12 to 18 carbon atoms.

7. A process as defined in claim 1 wherein said component C is added tosaid slurry in an amount at least twice the weight of said component A.

8. A process comprising adding to an aqueous slurry containing anN-higher fatty acid taurine compound and an alkali metal chloride, anamount of higher fatty acid of 12 to 18 carbon atoms sufiicient to forma compatible solvent system with the said taurine compound, heating theresulting mixture to distill off the water, and then separating thecrystallized alkali metal chloride from the mixture at a temperatureabove the solidification point of the solvent system containing the saidtaurine compound and the higher fatty acid.

9. A process as defined in claim 8 wherein said higher fatty acid iscoconut fatty acid.

- 10. A process as defined in claim 8 wherein said higher fatty acid istallow fatty acid.

11. A process as defined in claim 8 wherein said higher fatty acid ispalmitic acid.

12. A process as defined in claim 8 wherein said higher fatty acid isadded to said slurry in an amount ranging from about 2 to 6 parts byweight per part of the said taurine compound in the slurry.

No references cited.

1. A PROCESS COMPRISING ADDING TO AN AQUEOUS SLURRY CONTAINING (A) ANN-HIGHER ACYL TAURINE OF THE FORMULA